Owing to its low power consumption, long service life and high reliability, LED is generally recognized in various fields of daily life and widely applied in electronic products, e.g., serving as indicators in circuits and instruments and back light of displays.
Chinese Patent CN101110460A discloses a LED epitaxial crystallization technology, in which, the LED is formed over two sides of a transparent substrate or with two LED epitaxial wafer layers, which have same or different structures and components. Therefore, the LED formed through epitaxial crystallization can produce same or different colored lights. The stack method in such patent mixes lights for LED chips of different wavelengths and belongs to single-side light emitting, which requires further wire bonding and cannot realize large-angle light emitting status.
Many lamps are to be designed with omni-directional light emitting angle, generally realized by a GaN-based structure over the sapphire substrate. Though transparent, non-conducting and poor dissipation have restricted usage of the sapphire. An omni-directional light source has to be made through packaging design. Besides, in illuminating bulbs, a dissipation module for LED dissipation makes it more difficult to fabricate omni-directional lamps.